RESEARCH PAPER NUMBER THIRTY-NINE
CEMENT DISPERSION AND
AIR ENTRAINMENT IN
CONCRETE PAVEMENT CONSTRUCTION
EDW. W. SCRIPTURE JR., PH.D.
I > I R E C 1 O R
Master Builders Research Labor Uo»*i^s
Copyright 1942 - The Master Builders Company
CONSTRUCTION of highways and other pave-
ments presents a peculiar and difficult problem.
The conditions to which such structures are
exposed are particularly severe and properties not of
primary importance in other work are required.
During the last ten years cement dispersion has
proved its value and economy in concrete construction
generally. More recently the value of incorporating
added air in concrete, particularly with reference to
decreased scaling and added resistance to freezing and
thawing has been recognized.
A product combining these two principles has now
been developed which combines the virtues of both.
This paper has been written with the objective of
acquainting highway engineers and others who would
be interested with the nature of this product, the
manner in which it functions, and the results which
can be secured.
Highway concrete differs in its require romconci - lerally
in certain respects. High transverse rod surfaces resistant
to wear and scaling are particularly neo
The incorporation of more than the normal amount of e
air in the mix contributes to greater workability
increased resistance to scaling, and improved dura
entrainment may be secured by use of a portlan<- cement
blend, a Vinsol resin cement, or the addition of a foaiv
certain advantages and disadvanta-
ge value of cement sion in concrete mixes has been es
1 over a period o - effective in improving the prope
of the concrete in both the md hare (
A material. HP-7. designed especially for highway or othe
ment construction h: developed by combining the mc
factory foaming agent with the most practical cement dis
agent. The advantages of both are realized and
a foaming agent are overcome.
HP-7 is an effective me: s .ring those properties which
have been sought from the use of portland-natural cement blends, from
A insol res fcs, and from certain admixtures. It is, however,
free from the disadvantages which these have. HP-7 may be
effectively with any type of cement or blend.
HP-7 appears to offer at least a partial solution and the most
satisfactory solution so far available to the problem of securing high
igth, prevention of scaling, increased durability, and improved
wear res s in pavement construction.
RELATION OF DISPERSION TO SPECIAI/CEMENTS
Table of Contents
Introduction . 6
Methods of Incorporating Air 7
Natural Cement Blends 8
Vinsol Resin Cements 9
Foaming Agents 10
( lement Dispersion 12
Dispersing Agents, Foaming Agents, and Protective Colloids . 13
Development of HP-7 15
Effects of HP-7 16
Kconomics of HP-7 13
Relation of HP-7 to Special Cements . 19
Relation of HP-7 to Admixtures 21
Test Procedure 23
CEMENT DISPERSION AND AIR ENTRAINMENT
IN CONCRETE PAVEMENT CONSTRUCTION
THE problem of concrete for highways presents some differences
from that of concrete for general structural purposes. Highways
are essentially large flat slabs of comparatively small thickness
which are exposed to rather severe conditions. They must be able to
carry heavy loads, to stand exposure to severe weathering conditions,
and must have a wear resistant surface. These are conditions not
usually encountered simultaneously in ordinary construction.
The requirements of highway concrete are relatively high trans-
verse strength to carry the loads, durability to resist attack due to
exterior exposure and such added adverse conditions as de-icing with
calcium chloride or salt, and avoidance of any phenomena which
might impair the strength or durability of the surface. While it is
usually possible to secure a satisfactory quality with respect to any
one property of concrete, it is often difficult to secure a combination
of properties which will be all that is desired. It is perhaps for this
reason that a great deal of investigation has been directed to high-
way concrete without as yet reaching any agreement on a wholly sat-
Two other properties of concrete are of some importance in high-
way work. Workability in this type of concrete is essential, as it is
in any other. There is usually little difficulty in securing adequate
workability with the mixes commonly used. Volume change is also a
factor in that, if excessive, undue cracking of the slab will occur. Ade-
quate reinforcing and proper location of joints will usually prevent
excessive cracking if a mix of any reasonable volume change is used.
To secure high strength, compressive or transverse, is not in itself
difficult. A mix of adequate cement content with a low water-cement
ratio will be required. Further, any influence which tends to interfere
with the hydration reactions or to impair the qualitv of the cement
paste structure will be undesirable.
Durability of the concrete as a whole is also not a serious problem.
A low water cement ratio is required but without undulv high cement
content.* High strength and low permeability will contribute to dura-
bility. Recently there has been considerable work on the introduc-
tion of small amounts of air into concrete bv various means. It ap-
pears to be fairly generally believed that a small increase in entrained
air adds substantially to durability. It seems probable that excessive
air entrainment is undesirable as the beneficial effects would be over-
come by the loss in strength.
To secure a satisfactory surface is a more difficult problem and
probably more important. In the first place the surface must have
1 Lewis H. Tuthill. J. A. C.I. June. 1939, page 589.
high strength to resist abrasion, in the second, high durability to with-
si and the weather and treatments applied to the surface. F. H.
Ja< kson ! of the Public Roads Administration, has summed up the
situation as follows:
"While a good deal of publicity has been given the matter of
scaling in New York State, I personally have seen considerable
scaling on concrete pavements in many other northern states.
The scaling is, I think, undoubtedly associated with freezing
and thawing and is, I believe, primarily the result of water gain
or segregation during placing. This results in the formation of
a thin porous layer on the top of the pavement which is an easy
prey to the action of ice and salts used for ice removal. It is
my opinion that the principal effect of the natural cement is to
reduce the amount of this water gain, thereby producing a more
uniform mix from bottom to top of the slab, and consequently
a denser surface. I do not think there is anything very mys-
terious about it. Furthermore, there may be other materials
thai will accomplish the same thing/'
METHODS OF INCORPORATING AIR
A number of means have been investigated recently, both in the
laboratory and by laying experimental roads for the entrainment of
air to improve the quality of the highway by reducing bleeding. These
include the use of blended cements, particularly portland-natural
blends, the use of cements ground with various grinding aids such as
rosin, beef tallow, stearates, and especially Vinsol resin, and the ad-
Hi to the mix of foaming agents, especially Orvus (sodium lauryl
sulphate). Each of these methods has its advantages and disad-
All the foregoing methods of incorporating additional air into the
mix have some effects in common. All necessarily lower the unit
weight of the concrete. All reduce bleeding markedly and produce a
more fatty or cohesive mix.
It seems immaterial whether the unit weight of the concrete is
increased or decreased as long as this is not an index of other prop-
es. In the case of the air-entraining methods decreased wei
up to a certain point, is a criterion of improved durabil
Reduction in bleeding can hardly be anything but beneficial. It might
be thought that increased cohesiveness or fattiness as an aspen
workability would be beneficial, but, with the methods of finishing
commonly used in highway work such does not appear to be the case.
The fattier mixes tend to pull and are more difficult to finish. To
secure reduced bleeding, however, it seems to be necessary to increase
The effects of air entrainment on bleeding are discussed by Powers*
as follows: —
"Some materials, when added to a mix or when ground with the
cement, cause the formation of a comparatively stable foam which
gives the mix a high air content. This has a pronounced effect on the
rate of bleeding through a reduction in the effective capillary area
** A.S.T.M. Proc, Vol. 38, 1938 — Discussion, page 352.
*The Bleeding of Portland Cement Paste, Mortar and Concrete — by T. C. Powers,
Research Laboratory of the Portland Cement Association — Bulletin 2.
per unit gross cross-sectional area and through the effect of the buoyancy
of the bubbles on the force causing bleeding. The effect of the air
can be established by treating it as if it were an aggregate added to
the paste, an aggregate having definite volume but negative weight.
"It will be observed that the entrained air effects very substan-
tial reductions in the bleeding rate and that the calculated values are
in good agreement with the observed except in the case of the highest
air content. This latter value was checked and the discrepancy found
not to be due to error. It is believed that, when the air content be-
comes sufficiently high, the bubbles, ceasing to act independently, tend
to merge their boundary films and knit the whole mass together by
means of surface tension forces. With this amount of air the paste
will 'stand up' like whipped cream. It is possible also that the effect
of added surface in reducing the hydraulic radius may be involved,
but this seems doubtful, for examination under the microscope indi-
cated that the bubbles were large enough to have a low specific sur-
face. It was for this reason that the surface effect was neglected in
developing the above equations.
'These tests on neat cement paste do not tell the whole story of
the effect of air on bleeding as it would be experienced in practice,
for in these tests the water-cement ratio was constant. In practice,
the use of a foaming agent in a given mix permits a substantial reduc-
tion in the water-cement ratio because of the fluidity of the air itself.
The effect of such a reduction in water, superimposed on the effects
expressed by equation 36, would result in a very low bleeding rate
as compared with that of the same mix made without the foaming
agent. It seems therefore that this method of reducing bleeding de-
es further study, especially in view of the recent tests which indi-
on of a high proportion of air by means of a
ases the resistance to frost action."
Each of the air entrainment methods is considered individually
Natural Cement Blends
Natural cements were produced prior to the development of port-
5. In the early days Portland cement was used as an
i natural cement concrete to improve the strength, espe-
The natural cements, as the name implies, are
produced from a naturally occurring "cement rock" which has a com-
position similar to that of the Portland cement raw mix. The cemen-
! i T !" of the "rock" are developed by burning to tempera-
fiat lower than the for production of port land
In certain respects natural cements are superior to normal port-
land cement, although they vary widely anions themselves. Because
natural cement imparts desirable properties to the concn
not necessarily imply that some other natural cement will do
wise. The advantageous properties of natural cements are a gre
degn r "fattiness" which reduces bleeding and seg-
regation, greater durability, and lower heat evolution
advantages are slower rates of setting and hardening, lower B1
at least until after very long curing, and a higher water • tnent
for a given i r cy.
1 here is no >nt on the causes tor the properties of natural
cements. It may be that the natural origin of the "cement ro
the lower burning temperature produce
er watei and hence fatl
hand, the properties of these cemei
linment of a higher proportion of air in the mix which h
in turn, ascribed to small amoui
purposeh included in the 1 1
• rved increases in durability mighl • •
reduced bleeding, which would help
: entrained uir More p
sible. The lower heal evolution, a
development , are 6b\ ion
Vinsoi Resin Cements
A number of materials I
reduce ih»* amount of grindii ent clinker to pi
of the required finen<
more or less effective are \ insol resin, i
and Others. In addition to i he function
tatinjj grinding, i hej also affect th< vhen
- in concrete wil h respect part i u
md t h«- i
The best known grinding rid oi
used to a certain extent is \ h
\\ hen porl land < i
mall amount of V insol i
I lj facilitated. \\ hat is more
Burner, a cement
of air and to be more cohesh e or fat ■ . In r
>und cements produ< • the
Of natural with Portland
t clii •
1 15 5
The \ 'insol cement suffers from tl
port land-natural blend in th
strength appears to be greater for the Vinsoi res
the blend and. moreover, it is permanent: that is. with long curing
the strength of the concrete made with a portland-natural blend will
probablv equal that of a straight portland mix. whereas the \ insol
resin cement will always show lower than normal strengths. Appar-
ently the loss in strength is directly related to the amount of air en-
trained. Some strength data on cement ground with and without
3 .1 resin are given in Table Xo. 1. It is especially to be noted that,
although the water-cement ratio is lower for the Yinsol resin cement.
due to the replacement of water by entrained air. the strengths are
markedly lower instead of higher as would be expected.
Another difficulty with Yinsol resin cements is that their behavior
tv variable. The effect of a given percentage of Yinsol resin, as
measured for example by the decrease in unit weight of the concrete
which is an index of the* amount of air entrained, seems to vary with
different cement clinkers: even with clinker from the same mill pro-
duced at differer. ^nation implies that the effective
of the Yinsol resin with respect to air entrainment. bleeding, segre-
gation, fattiness, durability, and strength will van'. In the present
e of our knowledge these variations are unpredictable. This means
that, because a certain percentage of Yinsol resin is ground with the
cement clinker, it does not : ily follow that the desired prop-
erties will be secured. A better criterion of the effectiveness of a
Yinsol resin cement would seem to be the drop in unit weight of con-
crete made with the cement in question compared with a similar mix
from normal portland cemer. seems to be a matter
of trial and error from one lot of cement to another.
\ 'insol resin cements have been offered and to some extent used
as a substitute for portland-natural cement blend, to produce similar
properties in the concrete mix, particularly increased fattiness and
Tendency towards scaling. They are competitive on a cost basis,
as neither adds substantially to the cost of the concrete. Considering
the variability of the Yinsol resin cement and the losses in strength
which may result it would seem that, if the quality of workability
:i either Yinsol resin cement or the portland-natural blend will
impart is desired, the choice would be on the latter.
Rosin, beef tallow, oil. and similar materials are very similar to
Yinsol resin. Lik< they also impair strength. On the whole,
such informatio: available would indicate that they are less
satisfactory than Yinsol resin and there is no evidence that they have
received any general acceptance although some experimental high-
v installations have been made.
A large number of organic compounds will produce foaming. They
decrease the surface tension of water and those which are highly effec-
tive in this respect are also known as wetting agents. Any material
• ill produce a stable foam will, when addecl to a concrete mix.
tend to increase the amount of air entrained.
s -sion x of the general nature of wetting agents and their
behavior is as follows: —
'"In general, wetting agents are more or less complicated chemical
molecules composed of two essential parts. One is termed 'hydro-
Trom A .meriean Cyanamid & Chemical Corp.
philic, and it is the portion which draws the agent into water or is
attracted to surfaces which are the more polar. The other part of the
molecule is termed 'hydrophobic/ and it tends to leave the water and
attach itself to or dissolve in an oil or other non-polar medium Such
a molecule will orient or align itself at the interface, so that the hydro-
phihc part will be in the water and the hydrophobic part in the or-
ganic phase. t The fundamental governing factor in such orientation
is the attraction of like atoms or groups of atoms for one another.
"Wetting agents belong to a group of a more general class of mate-
rials called 'surface active agents,' and among their properties is their
ability to lower surface tension and interfacial tension. Surface ten-
sion values of solutions of a wetting agent are a measure of the effec-
tive amount of the material collected at the air-solution interface;
whereas interfacial tension values are a measure of the amount of
material collected at the liquid-liquid interface and consequently are
a measure of its surface activity.
"Surface activity is a special property and will vary from inter-
lace to interface. That is to say, because a wetting agent may be help-
ful in causing water to wet a hydrophobic material, it does not neces-
sarily follow that it will be effective in promoting better wetting of
a hydrophihc surface. Since conditions at the liquid-liquid interface
more nearly approximate the conditions under which wetting agents
are used, it is a fact that interfacial tension values are a more exact
indication of wetting action than are surface tension values.
"The degree of surface activity of such an agent depends primarily
upon the ratio of its hydrophilic to its hydrophobic constituents. This
ratio or 'balance' is markedly affected by the nature of these antago-
nistic groups and by their relative position in the molecule. Advan-
tage is taken of the factors influencing balance to formulate products
suitable for specific purposes. The presence, concentration, and chemi-
cal nature of other ingredients in the system determine to a large ex-
tent the final hydrophilic-hydrophobic balance of the agent."
With respect to decreased unit weight, decreased bleeding, and in-
creased durability, the effects of a foaming agent are essentially the
same as those of a portland-natural blend, or of a Vinsol resin cement.
With respect to the other properties of the concrete, foaming
agents vary widely. Many of them seem to interfere with the hydra-
tion reactions of the cement, thereby decreasing strength and possibly
increasing permeability. It is possible, however, to select a foaming
agent which does not impair the normal reactions of the cement and
of these Orvus appears to be the most suitable.
By addition of Orvus to the concrete mix the same effects with
respect to unit weight, bleeding and durability can be secured as with
a portland-natural blend. Unlike the latter, strengths are not im-
paired and instead of increased water-cement ratio for a given con-
sistency the required water is appreciably reduced. Further, lauryl
sodium sulphate is a definite compound so that its properties remain
constant as is not true of different brands of natural cement and pos-
sibly even of different lots of natural cement from the same source.
As compared with a Vinsol resin cement, addition of Orvus to the
mix will have similar effects with respect to reduction of unit weight,
bleeding and water requirement, and increased durability and cohe-
siveness. Unlike the Vinsol resin cement, it does not impair the
strength but should show some increase at all ages. Again, being a
definite compound, it is not subject to the variability of Vinsol resin
The principle of cement dispersion has been fully discussed in
Research Papers Xos. 35 and 36, but a brief review of this subject is
When portland cement is mixed with water, the individual par-
ticles tend to gather together and stick to each other in clumps, i.e.,
the solid-liquid system is flocculated. This is due to lack of mutually
repellent electrostatic charges on the cement particles. If a suitable
dispersing agent is introduced into the mix, the clumps are broken
up and the cement then acts as individual particles, i.e., is dispersed.
Dispersion of the cement produces two important effects. The
water which had been trapped within the particle clumps is released
to become a part of the mixing or placing water. The surface area of
the cement in contact with water is greatly increased, since the par-
ticles are no longer in contact with each other. As a result of the
first the amount of water required in the mix for a given consistency
is less, i.e., the water-cement ratio is reduced. Since the value of the
cement is dependent on a hydration reaction which is a surface phe-
nomenon, the second effect which promotes more rapid and more
complete hydration permits more efficient utilization of the cement.
By the reduction in water-cement ratio and by the increase in sur-
face area of cement available for hydration, the potential value of the
cement is more completely realized.
Those properties of concrete which are dependent on the surface
area of the cement and on water-cement ratio, and this includes most
of them, must necessarily be improved by dispersion. These effects
are realized in the concrete in both its plastic stage and subsequent
During the plastic stage, dispersion of the cement in a given mix
will produce more placeable concrete with less water, due to the re-
lease of water from the cement clumps. The fattiness of the mix is
increased, wiiile segregation and bleeding are reduced, due largely to
the increased effective surface area of the cement. Volume change
before hardening is markedly decreased, due in part to the lower water
content and in part to the greater surface area.
A greater uniformity and freedom from gross defects of the hard-
ened concrete may be expected from the improved properties in the
plastic stage. Greater watertightness with reduced permeability and
absorption are realized through the lower water content required for
placing. Higher strengths and greatly increased durability with re-
spect to both freezing and thawing and sulphate corrosion may be
attributed to the lower water-cement ratio of the dispersed mix' and
to the increased surface area available for hydration.
Although dispersion of the cement will accomplish most of the
effects of foaming agents and portland-natural blends or Vinsol resin
cements including decreased bleeding, increased durability, and in-
creased cohesiveness, it attains these results by an entirely different
means. Furthermore, it produces these effects without the disad-
vantageous properties of those methods which entrain large amounts
of air but with other advantageous properties of its own.
Cement dispersion does not produce its effects by the incorpora-
tion of large amounts of air but by reduction of water-cement ratio
and by making available for hydration or water retention a larger
surface area of the cement. By using a cement dispersing agent, the
unit weight of the concrete is not reduced appreciably (depending on
the type of mix and method of handling a dispersed cement mix will
show slightly higher or slightly lower unit weight than a comparable
undispersed cement mix). Since dispersion permits a reduction in
water for a given consistency, this means that in most cases there
will be somewhat higher air entrainment with the dispersed cement
but this is not large and is not of a magnitude comparable to the
effect secured with a foaming agent.
DISPERSING AGENTS, FOAMING AGENTS and
At this point it may be well to point out the very definite differ-
ences between dispersing agents, foaming or wetting agents, and pro-
tective colloids. They might be considered in relation to any solid-
liquid system, but for present purposes the discussion may be con-
fined to water as the liquid since cement is a typical solid-water system
in which the solid reacts with the liquid.
A dispersing agent is a compound which, presumably by adsorp-
tion in an oriented manner, causes the particles of the solid in suspen-
sion in the liquid to become mutually repellent, presumably because
they are thereby endowed with like electrostatic charges at the sur-
e. Dispersing agents are specific: that is, a compound which is a
dispersing agent for one solid-liquid system may or may not be a dis-
persing agent for some other system. Dispersing agents may or may
not lower or raise surface tension. They may or may not cause foam-
ing. The most satisfactory dispersing agent for cement in water has
a small but not marked effect in decreasing surface tension and does not
cause formation of stable foams. Dispersing agents, used in the pro-
portions suitable for dispersing cement in water, do not interfere with
the hydration reactions of the cement.
Foaming or wetting agents greatly lower the surface tension of
water. They form stable foams. They are not dispersing agents for
cement in water. Used in moderate quantities to produce air en-
trainment, at least some of them do not interfere with the hydration
reactions of the cement; others probably do. One case is known of
a foaming agent which is also a cement dispersing agent, but this
would seem to be a fortuitous combination as there is no necessary
relation between these two actions.
The difference between the action of a cement dispersing agent
and a foaming or wetting agent in water is illustrated in Fig. I.
Protective colloids will stabilize a suspension of a solid in a liquid,
that is, the protective colloid will be adsorbed on the solid particles,
preventing these from coming in close contact and hence preventing
to some extent coalescence. A protective colloid will stabilize a solid-
liquid system in which the solid is already dispersed by a dispersing
agent or other means. In a flocculated system the protective colloid
"*- In tube containing the
foaming agent, note form-
ation of a stable foam,
~ is absent in
containing the dispersing
In this manner the foaming
agent introduces a large
quantity of air into the mix.
will stabilize the system in the flocculated condition. Protective col-
loids do not have any large effect on surface tension and are not gen-
erally dispersing agents. Therefore, a protective colloid added to a
cement-water system does not produce dispersion. Some particular
protective colloid may also be a cement dispersing agent but this is
rare and is perhaps better stated that some dispersing agents for ce-
ment may also be protective colloids. Protective colloids are not in
themselves active foaming agents but they do tend to stabilize foams.
The adsorption of a layer of protective colloid on the surface of the
cement particles appears to interfere with hydration.
A suspension of cement in water may be termed a rather gross
colloidal system. Only a small portion of the cement particles of
smallest size are really of colloidal dimensions and will stay suspended
indefinitely. The effects of dispersing agents, wetting agents, and pro-
tective colloids are therefore less marked and less clear cut than they
would be in a truly colloidal system. This is a matter of degree rather
than of the nature of the phenomena. The finer the cement is ground
the more closely its behavior will resemble that of a true colloidal
system and for this reason the effects of a dispersing agent are more
marked with a fine cement.
It is also true that as commonly used in a concrete or mortar mix
the cement and water are in such proportions that they form a paste
rather than the dilute suspensions usually employed for the study of
colloidal phenomena. The solid particles no longer move as freely
in the liquid medium. There is, however, no doubt that^ the same
phenomena occur, although they may manifest themselves in a some-
what different manner. For example, dispersion has a, marked effect
in lowering the viscosity of a suspension of a solid in water having
in the flocculated condition a viscosity appreciably higher than that
vater. As the suspension becomes more dilute and in any condi-
tion, flocculated or dispersed, approaches the viscosity of water, this
effect becomes less marked and as the suspension becomes more con-
centrated and higher in viscosity it becomes more pronounced. These
are well known effects which have been observed in clay and other
suspensions and put to practical application in casting with clay slips
and in similar processes. In such solid-liquid systems the relation be-
tween dispersion, viscosity and adsorption can be followed through
alternate cycles of flocculation and dispersion. Similar phenomena are
exhibited by suspensions of cement in water of paste consistent.
DEVELOPMENT OF HP-7
The benefits to concrete of cement dispersion have been estab-
lished in this and other laboratories and in the field during a develop-
ment which has extended over more than ten years. The advantages
derived through the application of this principle to the properties of
concrete generally have been described elsewhere (Research Paper
No. 35) as has also its economic value (Research Paper Xo. 36). These
advantages are equally applicable to highway concrete generally, but
there remained the possibility that, to fit the special requirements of
highway work, other principles could be applied which would more
nearly approach a solution of this special problem.
Within recent years the desirability of incorporating somewhat
more air in concrete than is ordinarily entrained has been investigated
in this and other laboratories. Now there appears to be little question
that certain benefits are secured by this means as described above.
Certain of the highway departments have pursued this subject some-
what further as has also the Portland Cement Association and a num-
ber of experimental roads have been laid using what may be called
air incorporating agents. The most satisfactory such material seems
to be Orvus (sodium lauryl sulphate) and at least one highway de-
partment has definitely reported that observations from a compari-
son of a number of experimental road sections have indicated that
this is the case.
The introduction of air into the cement paste is undoubtedly at-
tended by undesirable effects, whether or not the benefits of so doing
outweigh the disadvantages. It appeared that a combination of the
principle of dispersion with that of air incorporation might solve these
difficulties. By dispersion of the cement it should be possible to over-
come the deleterious effects of air incorporation and to superimpose
the benefits of cement dispersion.
From these considerations HP-7 was developed. It is essentially
a combination of the best air incorporating agent, sodium lauryl sul-
phate, with the most satisfactory and economical cement dispersing
agent, a derivative of lignin sulphonic acid.
EFFECTS OF HP-7
As would be expected from its composition, HP-7 produces two
effects, that of a dispersing agent and that of a foaming agent.
The effects of a dispersing agent on a concrete mix are those which
have been described elsewhere. They are essentially as follows: —
A. In the plastic state of the concrete: —
1. More placeable concrete with less water
2. Increased fattiness
3. Reduced segregation and bleeding
4. Greater water retentivity
5. Reduced shrinkage before hardening
B. In the hardened concrete:—
1. Increased durability
2. Increased watertightness
3. Higher strength
4. Lower volume change
5. Lower permeability and absorption
6. Greater uniformity and freedom from gross defects
The effects of the introduction of additional air by means of a
foaming agent are essentially as follows:—
A. In the plastic state of the concrete: —
1. Increased fattiness
2. Reduced bleeding
B. In the hardened concrete:—
1. Increased durability
2. Greater uniformity and freedom from gross defects.
3. Strength unaffected by a suitable foaming agent but
reduced by others.
With respect to fattiness and bleeding, the dispersing agent and
the foaming agent reinforce each other. The same is true of dura-
bility and uniformity of the concrete. The dispersing agent overcomes
any tendency of the foaming agent to lower strengths by diluting the
cement paste with air and actually produces increases in strength.
As a consequence HP-7 attacks the problem of improving high-
way concrete at those points which have, in the past, been the most
vulnerable. The effect on durability and bleeding is illustrated by the
results of freezing and thawing (with calcium chloride) tests shown in
Fig. II. The effects on strength are shown in Table II. It is hardly
possible to express fattiness or freedom from gross defects quanti-
ely but there can be little doubt, as has been shown by numer-
ous qualitative observations by many different observers, that HP-7
does markedly improve these properties.
Effects of Freezing and Thawing (with calcium chloride) on the
surfaces of slabs. The same concrete mix at the same slump was used
in each case.
HP-7 1# sk
HP-7 1 # sk
HP-7 1 # sk
Plain With iir :
Lbs. In. Lbs. per sq. in. per
\\ ater Slump 3 days 7 days 28 days Sack
21.56 2i. 1420 2140 3410 8.0
18.44 3 1770 3090 4080 6.9
21.31 2% 1560 2350 3290 8.0
17.63 1840 2550 3670 6.6
21 69 -V j 1310 2020 2940 8.15
17.88 2y 2 1880 2850 3700 6.75
- Cement (Portland I 30 lbs.
Sand. 90 lbs.
Stone V 133 lbs.
ECONOMICS OF HP-7
The actual cost of the materials which compose the concrete mix
used for highway concrete is undoubtedly only a very small portion
of the total cost of highway construction. The cost of any material
which had even a small influence in prolonging the life of the con-
crete and which caused only a small percentage increase in the cost
of these materials would be amply justified. The increase involved
in adding HP-7 to an ordinary highway mix would amount to about
i if the cost of the materials and this might be estimated as amount-
ing to not more than 0.1^ of the total cost of the highway. If even
increase in the life of the concrete were secured by this means,
the expenditure would be well warranted.
This is not, however, the situation. Life of the concrete is increased
to a vastly greater extent and this increase can be secured at no
additional cost. The cost of adding HP-7 to the average highway
concrete mix amounts to about the equivalent of the addition of
1 2 additional sack of cement. The greatly increased durability of a
mix with HP-7, costing approximately the same as a similar mix
without HP-7, is illustrated in Fig. III.
Effects of Freezing and Thawing (with calcium chloride) on the
surfaces of slabs. The plain mix is at the same consistency as the mix
with HP-7 but contains ] 2 sack additional cement per cubic yard.
Y\ ith respect to the other properties of these two mixes, the strength
is not decreased but increased Table III . Permeability and adsorp-
tion are decreased. Volume change is reduced. Segregation, shrink-
age before hardening, are decreased. Uniformity, watertightness,
water retentivity, and placeability are increased.
3 means essentially that, at a given cost, the quality of the
concrete is improved by the incorporation of HP-7 and that as a con-
tence a highway of longer life with greater freedom from scaling
is secured at no additional expense.
Compressive Strength Gals,
SERIES I Lbs. In. Lbs. per sq. in. per
Addition Water Slump 3 days 7 days 28 days Sack
Xone 21.56 2' > 1420 2140 3410 SO
10% less cement 18 . 31 2* , 1450 2460 3360 7 . 65
Xone 21.31 2 ; , 1560 2350 3290 8.0
HP-7 lr sk-
10' ; less cement 17 . 38 2 , 1730 2520 3610 7 . 25
Xone 21.69 2'> 1310 2020 2940 8.15
HP-7 1^ sk-
10% less cement 17.56 2y 2 1730 2570 3560 7.35
HP-7 l#/sk —
13' < less cement 17.56 3 1290 2000 2970 7.65
Concrete Mix - Cement (Portland) 30 lbs.
Sand 90 lbs.
Stone (%") ....133 lbs.
Normal Portland Cement
Cement -- lbs 574 4!»!»
Sand - lbs 1134 1123
( travel - lbs 2099 2070
Water - gals 31.2 28.2
Slump - in V/i 2}i
( Jompressive Strength —
Lbs. per sq. in.
delays 2630 2250
7 days 2790 2910
28 days 3430 3750
RELATION OF HP-7 TO SPECIAL CEMENTS
The only special cements which have been proposed for highway
work are the portland-natural blends and cements ground with a
grinding aid such as Vinsol resin. The effects of these have been de-
HP-7 will produce similar effects to those of portland-natural ce-
ment blends and will further give results not obtained with these.
With HP-7 the increased water-cement ratios of natural cement blends
for a given consistency are not required but decreases are secured.
The early strengths are not impaired but increased. The variability
encountered with different natural cements is not encountered and a
definite controlled result is produced.
In addition the desirable properties which spring from a decreased
water-cement ratio such as lower volume change, increased strength,
and increased watertightness are realized. There would seem to be
no question that, for a given result, the more desirable means of se-
curing it, as compared with a portland-natural blend, would be the
use of HP-7.
There is, however, another way of looking at this question. Natu-
ral cement blends undoubtedly have beneficial effects on highway
concrete which seem to outweigh their disadvantages. It may seem
desirable to use such a blend. In this case HP-7 will have the same
advantages in a portland-natural blend as it will have in a straight
Portland cement mix. Strengths will be equal or greater (Table IV),
bleeding will be further reduced and durability increased, (Fig. IV).
Here also volume change will be decreased, watertightness and other
Cement — lbs.
Sand - lbs.
• • sq. in.
< Concrete with HP-7
Purl land Blend plain
i qua! consistency slump .
*lend Portland <s:}i,/,
l 7 v
Thawing with calcium
m 1 *
In comparison with Vinsol resin cements, the situation is much
the same Fig. V . The same effects can be produced at the same
or less cost. Further, other properties such as volume change, water-
tightness, and so forth, are improved. The Vinsol resin and similar
ally show losses in strength if they are effective in incor-
porating air. If they are not effective in this respect they are useless.
HP-, increases in strength, consequently, for a given strength,
pressive or transverse, a concrete mix with HP-7 can be produced
at definitely lower cost. It should not be overlooked that for highways
transverse strength is an important factor in view of the loads which
ways are required to carry.
Effects of Freezing ,and Thawing (with calcium chloride) on the
aces of slabs. All mixes are of the same design and at the same
All the cements are made from the same clinker and
have equal surface area ( 1660 sq. cm. per g).
; i .Mm v w * C, *
' H AT 28 DAYS,
4^0 LBS. PER SQ. IX.
strength at 23 days,
3210 lhs. per sq. in.
D WITH .032
Vinsol Resin, compres-
sive STRENGTH AT 28 DAYS,
2660 LBS. PER SQ. IN.
Airain, from the other point of view, HP-7 can be used in conjunc-
tion with a Vinsol resin cement or similar cement to produce the de-
sired properties in a higher degree and at lower cost. In this case,
however, care should be taken to design the mix in such manner that
an excess of air is not introduced.
RELATION OF HP-7 TO ADMIXTURES
The part played by admixtures has been discussed at some length
in Research Paper Xo. 38. As far as highway construction is con-
cerned the only admixtures which might be of interest are those foam-
tgents which incorporate additional air.
In some cases high early strength is a factor so that calcium
blonde might be considered as also high early strength ce-
ment and additional cement. These topics in their relation to
ement dispersion are discussed in Research Paper Nos. 36
The foaming agents undoubtedly offer some advantages with re-
spect to air inclusion as it improves durability and reduces bleeding.
This has been discussed above. HP-7 includes a suitable proportion
of the most satisfactory foaming agent. In addition it applies the
principle of cement dispersion to highway concrete, thereby over-
coming the disadvantages of foaming agents alone and adding the
benefits of cement dispersion.
HP-7 is a combination of those two principles which seem to offer
the greatest chance of solving the problem of durable wear resistant
highways. The employment of a foamine agent causes increased air
incorporation and thereby increases fattiness, durability, and resist-
ance to scaling and decreases bleeding. The application of cement dis-
persion offsets the disadvantages of a foaming agent such as diminished
strength, increased volume change and possibly increased water-cement
ratio. It further yields the advantages to be derived from reduced water-
cement ratio and more effective use of the cement by making an in-
creased surface area available for hydration.
Economically, the use of HP-7, by designing the concrete mix
with this material, permits all the advantages of cement dispersion
and air incorporation to be secured at no additional cost.
In comparison with certain special cements such as natural-
portland blends, or grinding-aid (Vinsol resin > cements, the same ad-
vantages may be secured at lower cost without the disadvantages of
these "cements. With these special cements themselves, HP-7 secures
not only the benefits of the special cements but adds to them.*
Admixtures in general do not produce the results of HP-7. Foam-
ing agents offer some of its advantages but have also some undesir-
able effects. Since HP-7 combines the best of the foaming agents with
cement dispersion, it produces results which cannot be secured with
admixtures generally and moreover at substantially lower costs.
• With these special cements it is possible that a cement dispersing agent
without foaming agent could be used to greater advantage than HP-7.
In order to determine the real value of HP-7 it is necessary to
carry out a testing program to show its effects on the properties of
the concrete and its economic value. For this purpose the following
program is suggested.
First select the most satisfactory mix which it is possible to design
from the materials available and using whatever cement seems most
advantageous. Then proceed as follows:—
A. Workability and Water Cement Ratio —
With selected mix make mixes and determine slump (and flow
if desired) with and without HP-7 at equal w c.
B. Stn ngth —
With selected mix make concrete mixes at equal slump (or flow)
as follows: —
1. Selected mix — plain
2. Selected mix with HP-7
3. Selected mix less 10% cement with HP-7.
Make cylinders for compressive strength determinations at suit-
able ages (7 and 28 days), making not less than three specimens
for each age. Make beam specimens for transverse strength if
( . Durability —
a Make block specimens from same mixes as under B, 10" x 10"
by not less than 5". Cure for 28 days and subject to freezing
and thawing with calcium chloride. For this purpose build
dike around edges of specimens with caulking compound,
putty or other suitable material. Cover with water and
freeze, remove from freezing chamber and thaw with fixed
amount of calcium chloride. Repeat this cycle until appre-
ciable deterioration of surface on plain mix is observed.
(b) Make cylinder or beam specimens from same mixes as under
B. Cure 28 days. Subject to freezing and thawing in satu-
rated condition. Determine deterioration at suitable inter-
vals by loss in weight, expansion or sonic method.
D. Water tightness —
Make specimens from mixes as under B, cubes, blocks, cylinders,
or cut specimens from test pieces made under B. After 28 days
curing allow to dry out in air. Weigh. Immerse in water and
determine weight at suitable time intervals until constant weight
E. Wear Resistance —
Make block specimens as in C-a from same mixes as given under
B. Make these specimens with smooth trowel finish. Test for
resistance to abrasion by any accepted method. (A good method
for testing abrasion resistance rapidly is described in the Journal
of the American Concrete Institute, Sept. -Oct., 1937, page 17.)
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